Magnetic Raisins

The common phenomenon of magnetism is familiar to most of us as the result of playing with magnets to pick up paper clips and nails. That strong effect goes by the name of ferromagnetism. There are two other types of magnetism unknown to most people. They are paramagnetism and diamagnetism. These two types are much weaker than ferromagnetism and go unseen. But, they exist and are observable under the right circumstances.

To demonstrate diamagnetism, I suspended dried raisins on the ends of a wooden skewer which was hanging by a fine thread. The assembly is very sensitive to twisting forces. I brought a very strong neodymium magnet close to the raisin at one end. Watch what happened.

The same effect occurred if the magnet was reversed. The raisin always repelled weakly. You might wonder if other things exhibit diamagnetism. What about a grape? This link takes you to a video by the Exploratorium in San Francisco. He tests a grape and even aluminum foil. The results might surprise you.

Water is a substance that exhibits diamagnetism. Objects consisting of nearly all water can be seen to repel from strong magnets. Scientists have even tested the effect on a living tiny frog. They were able to levitate the frog in a strong magnetic field. It suffered no ill effects.

If you are more curious and would like to see some explanation of these magnetic effects, watch this video from Khan Academy.


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